1. Field of the Invention
This invention relates in general to threaded fasteners, and in particular to a screw that forms threads as it is inserted into a hole.
2. Description of the Prior Art
A thread rolling screw is a fastener that has threads specially configured so that it will form threads as it enters a hole. There are several types. One type has a cross section that resembles a triangle with rounded corners. Only three points on the screw thread will be at full diameter. The spaces of lesser diameter between these points reduce the torque required to rotate the screw into the hole. A disadvantage is that it does not provide the full holding strength of a screw that has a continuous circular full diameter thread.
Another type utilizes a tip portion with a plurality of threads of increasingly larger diameter. These threads are not continuously circular. That is, one or more recesses or relieved areas will be located on the crest of each thread. These recessed areas reduce friction during the process of installing the fastener in the hole. The reduced friction reduces the torque. While workable, it would still be desirable to further reduce the torque, yet provide good holding strength. Also, the type having a single large notch extending up the first few threads tends to create chips when forming the threads in the hole. Loose chips can create problems with electronic equipment.